The prevalence of childhood obesity in the United States has tripled to 17% since 1980. Recent human and animal studies have demonstrated that maternal obesity increases the risk of offspring obesity, which indicate that fetal programming plays an important role in the obesity epidemic. The ultimate goal of this project is to elucidate the underlying mechanisms through which maternal obesity alters the intrauterine metabolic environment and programs offspring obesity. Adiponectin is an adipocyte-derived hormone that sensitizes insulin and regulates energy homeostasis. Blood adiponectin levels of newborns are 4-7 folds higher than that in maternal circulation. In contrast to adults, neonatal blood adiponectin concentrations positively correlate with infant body weight. Studies have shown that adiponectin enhances adipocyte differentiation, inhibits lipolysis and increases adipose tissue mass in mice. Consistent with human studies, our preliminary mouse studies showed that maternal obesity significantly increased fetal body weight. Although there was no change in placenta mass, remarkably increased lipoprotein lipase (LPL) gene expressions were observed in placentas from obese dams. Blood adiponectin concentrations were also significantly increased in fetuses from obese dams. Importantly, adiponectin gene deletion attenuated maternal obesity-induced high birthweight and placental LPL expression. Furthermore, mouse embryonic fibroblasts (MEFs) from obese dams exhibited remarkable high efficiency in adipocyte differentiation, while protein levels of transcription factor C/EBP2 was significantly elevated. A methylation region was identified in the promoter of C/EBP2 gene. The methylation levels of C/EBP2 promoter were significantly low in MEFs from obese dams. Adiponectin treatment increased C/EBP2 gene expression while reduced its DNA methylation in MEFs. Therefore, we hypothesize that elevated fetal adiponectin mediates maternal obesity-induced high birthweight and offspring obesity by increasing placental fatty acid transport and reducing C/EBP2 gene methylation. Studies of Specific Aim 1 are designed to determine the role of fetal adiponectin in maternal obesity-induced high birthweight and adult obesity using a series of mouse models, which take the advantage of the in-transportablility of adiponectin through placenta and create a unique model with intrauterine adiponectin deficiency. Specific Aim 2 will study the effects of fetal adiponectin on placental fatty acid transport. A placenta-specific LPL knockout mouse model will be employed to verify the role of placental LPL in maternal obesity-induced high birthweight and adiponectin-enhanced fetal lipid accumulation. By using high fat diet-induced obese dams and adiponectin knockout mice, Specific Aim 3 will study the effects of maternal obesity and the role of fetal adiponectin on C/EBP2 promoter methylation. Overall, this project will investigate the role of fetal adiponectin in maternal obesity-programmed offspring adiposity. These studies will reveal new pathways of fetal programming that will lead to new therapeutic approaches to stop the vicious cycle of maternal-offspring obesity.